I. Field of the Invention
The present invention relates generally to the field of chemistry. More particularly, it relates to synthetic methods, intermediates and catalysts for the synthesis of pharmaceuticals, including (−)-Nutlin-3.
II. Description of Related Art
Small molecules are attractive tools for drug development due to the ease with which they can be diversified structurally and functionally to optimize for potency, selectivity, and therapeutic window, while offering the long term possibility for large-scale production at relatively low cost. Chiral small molecules often provide versatility beyond achiral variants when attempting to disrupt the interaction between a peptide and its chiral receptor protein, but the additional stereochemical complexity can render a preparation long and cumbersome, or dependent on chromatographic techniques. A current case where a mismatch exists between therapeutic value and synthetic access is Nutlin-3, a chiral imidazoline discovered by Hoffmann-La Roche that inhibits p53-MDM2. Dubbed the ‘Nutlins’ as a general class of cis-4,5-disubstituted imidazolines, these small molecules have been in development as chemotherapeutics, and have emerged as powerful tools for the interrogation of a wide range of cellular signaling pathways. Although (−)-Nutlin-3 is >150 times more potent than its enantiomer ((+)-Nutlin-3), Nutlin-3 and its derivatives are still produced as the racemate, subjected to preparatory chiral chromatography, and the less active enantiomer—50% of the material synthesized—is discarded.
Inhibition of the oncoprotein MDM2 by a small molecule was validated as a strategy in 2004 when Vassilev and coworkers at Hoffmann-La Roche (HLR) reported that a class of chiral cis-4,5-disubstituted imidazolines (e.g., 1, dubbed the ‘Nutlins’) inhibit p53/MDM2 binding in vitro (Vassilev et al., 2004; Vassilev, 2004; Carvajal et al., 2005; Fry et al., 2005a; Fry et al., 2005b).

The p53 tumor suppressor network is autoregulated by MDM2, and for the approximate 50% of human cancers in which the p53 gene is wild-type, restoration of p53 and its associated network provides the cell with a pathway to apoptosis (Harris, 2006; Fischer and Lane, 2004; Bond et al., 2005). Furthermore, MDM2 is related to cell proliferation and survival through a range of interactions with additional proteins (Lowe et al., 2004). A rough estimate of the impact of the Nutlins might be assessed by noting that over 800 publications have cited the 2004 HLR paper in the intervening six years. In addition to their potential as biochemical probes and chemotherapeutics, the Nutlins provided a novel chemical scaffold from which to design small molecules that might rationally mimic the helical backbone of a peptide (Vassilev et al., 2004). This hypothesis was supported by X-ray crystallography of an MDM2-Nutlin complex in which the imidazoline occupied the native p53 ligand binding site.
As a chemotherapeutic, Nutlin-3 ultimately became the lead drug candidate, and ‘enantiomer-a’ binding was measured at 90 nM, about 151 times greater than its antipode ‘enantiomer-b’ (Vassilev et al., 2004). Despite the excitement surrounding the study of these small molecules as probes of cellular biology, supply issues for this chemotherapeutic currently limit its use on a larger scale, and the broader evaluation of the chemical biology of chiral nonracemic cis-imidazolines. Nutlin preparative details have been restricted to a series of patent disclosures to-date, and the absolute configuration of ‘enantiomer-a’ was suggested in a recent patent (U.S. Publn. 2005/282803). (−)-Nutlin-3 is available commercially from Cayman Chemical for approximately $85/mg. As the Nutlins migrate forward from their current preclinical position, the quantity of material needed for each phase will increase substantially.
One of the currently favored synthetic approach to the Nutlins (FIG. 1) illustrates how the underlying symmetry of the target was leveraged to prepare symmetrical (as amidine tautomers) imidazoline 6 in a concise manner (PCT Appln. WO 03/051359). The key cis-diamine 5 was prepared using a diaza-Cope reaction (Kim et al., 2008) from cis-diamine 4 (Vögtle and Goldschmitt, 1976). Although Nutlin-3 (1) is obtained after a single further transformation, it is formed as a racemate that requires a subsequent resolution. While this was possible for Nutlin-3 using expensive preparatory supercritical fluid chromatography equipped with a chiral stationary phase (Wang et al., 2007). In addition to the financial drawback associated with the separation, (+)-Nutlin-3 is a significantly weaker inhibitor of p53-MDM2, rendering this synthesis approach rather wasteful since the coproduction of the less potent enantiomer doubles the quantity of material at every step of the synthesis. Furthermore, a stoichiometric amount of cis-diamine 4 is required to prepare cis-diamine 5, and the use of a diaza-Cope reaction in this manner can efficiently furnish only symmetrical progeny. Therefore more practical methods for the synthesis of (−)-Nutlin-3 would be a great advantage.